1. Field of the Invention
The present invention relates to a metal organic chemical vapor deposition (hereinafter referred to as "MOCVD") apparatus and to a deposition method. More particularly, the present invention relates to an MOCVD apparatus useful to deposit high dielectric thin film on a semiconductor substrate and to a deposition method using the same.
2. Description of the Prior Art
For the next generation DRAMs which are at least 1 Giga in memory size, conventional thin films not supply enough capacitance. As semiconductor devices scale down, three-dimensional capacitor structures, such as fin and cylinder type structures, are more difficult to construct because the scaling-down is accomplished at the sacrifice of cell area reduction.
In addition, reduction in the thickness of the thin film gives rise to an increase in leakage current at a source/drain region, an impurity region of a semiconductor device, and causes a soft error, a phenomenon wherein the information stored in a capacitor is changed or lost by .alpha.-particles. So, a reliable capacitor is difficult to obtain. Further, if a capacitor is formed into a complex three-dimensional structure, subsequent processes are hard to perform.
Recently, active research has been directed to a high dielectric thin film deposition apparatus in order to apply high dielectric materials, such as BST (BaSrTiO.sub.3) and SrTiO.sub.3, for the thin film of a capacitor.
To construct high dielectric thin films, many methods are used, including a sputtering method, a sol-gel method, a laser ablation method, an MOCVD method, etc. Of them the MOCVD method guarantees a uniform thin film as well as allows the composition of the thin film to be easily controlled. Accordingly, the high dielectric thin film deposition apparatuses which utilize the MOCVD method are now being actively researched.
In order to better understand the background of the invention, a description will be given of a conventional MOCVD apparatus and its operation procedure, in conjugation with FIG. 1.
As shown in FIG. 1, a typical MOCVD apparatus comprises a reactant source ampule 10, a liquid micro pump 20 for delivering the reactants, a vaporizer 30, a reactor 70, a trap 60 and a vacuum pump. The reactants contained in the source ampule 10 are dissolved in a solvent. The liquid micro-pump 20 is used to transfer the resulting liquid to the vaporizer 30 in which the liquid is heated or vaporized with the aid of another energy source. Using a carrier gas, such as argon or nitrogen, the vapor is transferred the reactor 70 and the vapor is deposited on a semiconductor substrate loaded in the reactor 70, to form a thin film. Here, pressure rising gas which is needed for the transfer of the reactants, is also argon or nitrogen.
During the transfer of the reactants dissolved in the solvent to the reactor, however, since the vaporization temperature of the solvent is much lower than that of the reactants, the solvent, although no heat is applied to the vaporizer, is separated faster than the reactants, recondensing the reactants. Accordingly, the recondensed reactants block the thin film transfer line between the vaporizer and the reactor and thus, are not constantly fed to the reactor. As a consequence, a deposited thin film is formed poor in properties.
Even when heat is applied to the vaporizer in order to constantly maintain the vapor pressure of the reactants necessary for the thin film deposition, the solvent is faster vaporized than the reactants, resulting in the decomposition of the reactants. Likely, the reactants cannot be constantly fed to the reactor since the decomposed reactants block the thin film transfer line between the vaporizer and the reactor. So, it is difficult to form a thin film reliable and excellent in electrical properties.